Known in the art is an injection apparatus in which a plunger for injecting a molding material in a sleeve into a mold is driven by a booster type injection cylinder (for example Patent Literature 1).
Such a booster type injection cylinder has an injection piston which is connected to the plunger and has a booster piston capable of pressurizing a hydraulic fluid (for example oil) behind the injection piston. Further, by supply of the hydraulic fluid from an accumulator or other hydraulic pressure source to the back of the injection piston, the plunger moves forward and the molding material in the sleeve is injected into the mold. That is, an injection process is carried out. Further, after the injection process, by supply of hydraulic fluid to the back of the booster piston, the hydraulic fluid behind the injection piston is pressurized by the booster piston, and consequently the molding material in the mold is pressurized by the plunger. That is, a boosting process is carried out.
The injection apparatus in Patent Literature 1 has a control valve for controlling the flow rate of the hydraulic fluid discharged from the front of the injection piston (valve configuring a meter-out circuit) for controlling the speed of the plunger. Further, to ensure the timing of start of boosting becomes a suitable one, the injection apparatus in Patent Literature 1 determines the timing of start of boosting based on the time when the speed of the plunger which has decelerated by receiving a counterforce from the molding material filled in the mold falls to a predetermined threshold value. When the timing of start of boosting arrives, the control device of the injection apparatus in Patent Literature 1 outputs a signal for opening the booster valve which controls the supply of the hydraulic fluid to the back of the booster piston and outputs a signal for changing the opening degree of the control valve to one for boosting simultaneously with this.